When running, the initial landing position of the foot (or initial contact foot strike as it is called) varies for different running styles. For example, a classical rearfoot striker lands on the rear outside or lateral border of the foot. Other runners (referred to as midfoot strikers) make initial ground contact closer to the midpart of the foot, and a few runners (referred to as straight heel strikers) land on the back of the heel rather than the lateral border.
Straight heel strikers, sometimes described as straight toe "Indian runners", typically have a 0.degree. toe out. Runners who make initial foot strike along the outsole's lateral border, however, typically toe out by a specific angle. Depending on the runner's particular running style, the toe out ranges from something slightly more than 0.degree. to about 30.degree.. The average toe out for runners who land on the outsole's lateral border is about 16.degree..
Furthermore, a runner, such as a rearfoot striker, who makes initial contact foot strike along the outsole's lateral border pronates about his subtalar axis after landing to plant his foot in a flat or pronated position on his forefoot. From the position on the forefoot, the runner rises up on his toes to propel himself forwardly.
Known outsole rib designs or patterns, which are used for traction, do not account for variations of toe out. Furthermore, known outsole rib patterns are not arranged to optimize traction and to reduce wear for an average toe out of about 16.degree., especially for initial foot strike at the lateral border of the sole.
Another significant problem with known conventional running shoes is that the bottom of the sole is typically flat or essentially flat and terminates in a relatively sharp, ground level edge along the lateral or outside border of the shoe in the region of initial foot strike. Rearfoot strikers therefore land on this edge before pronating to a flat forefoot position. Although this edge deforms to some extent under the runner's load, it nevertheless creates an artificial fulcrum which promotes an unstable landing as well as causing the foot to pronate abruptly into a flat position with a significant impact.